Trucks having truck beds are sometimes used to transport sensitive items that must be cushioned from severe mechanical shocks. Conventional mattress arrangements that are used on truck beds today are ill-suited for this task at least because items placed on such mattresses may be subjected to sliding or rolling impact with the inner sides of the truck bed during turns and periods of acceleration and deceleration. The shortcomings of conventional mattress designs can be even more conspicuous in military applications where such sensitive items may also need to be protected from intentional harm, where the truck may be operating on unimproved roads or other uneven surfaces, and where the truck operator may experience periods of distraction from the effort to drive the truck smoothly. Thus, there is a need in the art for an improved mattress design for use on truck beds.